Method of discharging a cloud



Nov. 8, 1966 H. Moss-:s ETAL.

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.56 l INVENTORS United States Patent O 3,284,686 METHOD OF DISCHARGING ACLOUD Harry Moses, Park Forest, and Ronald L. Martin, La

Grange, Ill., assignors to the United States of America as representedby the United States Atomic Energy Commission Filed May 5, 1964, Ser.No. 365,223 3 Claims. (Cl. 317-262) The invention described herein wasmade in the course of, or under, a contract with the United StatesAtomic Energy Commission.

This invention relates to methods of discharging clouds and moreparticularly to a method of discharging a cloud using a charged particlebeam.

A cloud in 'general is highly charged with respect to the earth, withrespect to different regions of itself, and with respect to -otherclouds nearby so that high electric fields exist therebetween. Underappropriate conditions, this charge or potential difference becomes sogreat that discharges occur spontaneously in the form lof lightningstrokes. When lightning Istrokes occur to the ea-rth, large amounts ofproperty damage may result therefrom. Moore, Vonnegut, Machado andSurvilas, J. Geophys. Res., 67, 207 (1962), have observed increasedradar echo development followed by heavy rainfall within a few minutesafter a lightning flash occurred within a given region. These authorsstate that the lightning flash probably contributes to the formation ofthe rain gush, by greatly enhancing the rate of coalescene of raindroplets.

Thus,vunder certain conditions it is desirable to prevent the occurrenceof lightning strokes either to stop attendant proper-ty damage ordecrease the probability of rainfall. Conversely by initiating alightning stroke from particular cloud formations, the probability ofrainfall therefrom can be greatly enhanced in .a particular area.

It is therefore an object of the present invention to provide a methodfor discharging a cloud.

It is another object of the present invention to provide a method fordischar-ging a cloud whereby the prevention or initiation of a lightningstroke therefrom may be accomplished.

Other objects of the present invention will become more apparent as thedetailed description proceeds.

In general, the present invention comprises generating a high energyparticle beam, determining a charge center o'f a particular cloud anddirecting the high energy particle beam at the determined charge centerof the cloud. The high energy particle beam creates `an ionized path inthe atmosphere to provide a low resistance path wherethrough the cloudwill discharge.

Further understanding of the presen-t invention will best be obtained byconsideration of the accompanying drawings in which:

FIG. l is a graphical representation of the ver-tical profile ofionization concentration produced by the beam from the Argonne ZeroGradient Synchrotron.

FIG. 2 is a sketch of an apparatus for the practice of the presentinvention.

FIG. 3 is a sketch of the apparatus of FIG. 2 showing in detail the beambending magnets and the control equipment associated therewith.

FIG. 4 is a cross section of the bending magnet of FIG. 3 taken alongline 4-4 thereof.

For clarity of understanding of the method of the present invention, theproton ybeam of the Zero Gradient Synchrotron at Argonne NationalLaboratory willvbe usedvin the description thereof. It is to beunderstood that the pre-sent invention is not to be limited to the useof this beam and, as will later be set forth in the specifi- 3,284,686Patented Nov. 8, 1966 ICC cation, other particle beams may be used toaccomplish the method thereof.

The Argonne Zero Gradient Synchrotron is designed to produce a pulsedproton beam having 1013 protons per pulse of 10 micros-econd duration,once every four second-s. Protons with energies ranging to 12.5 bev. arepossible. At the exit, the beam has a cross-sectional area of about 50cm?. With suitable bending magnets, as will be shown later, it ispossible to turn the accelerator beam into the atmosphere and -to aim itin a predetermined direction.

According to Aron, Hoffman, and Williams, Range Energy Curves, ABOU-663,TID, Oak Ridge, Tennessee, l950,a beam of 3 bev. protons loses roughly 2mev. per gram per square centimeter of dry air. This energy loss isreferred to as the specific rate of energy loss; and if it is multipliedby the density of air (l.25 lO3 grams per cubic centimeter), the actualrate of energy loss for particles of that ener-gy value is obtained.That is, protons having an energy of 3 bev. will lose 2.5 103 mev. percentimeter (or 0.25 mev. per meter) of air traversed. Assuming normaltemperature and pressure conditions, the proton beam will pass throughabout 8 meters of atmosphere before losing 2 mev. of energy. Thisassumes no cataclysmic condi-tions are involved. Since a homogeneousatmoshpere at common ambient temperatures has a height of about 8kilometers and taking into consideration the gyrations of a high energyproton beam around the earths magnetic lines of force, a proton beamhaving energy greater than 3 bev. will pass through most of the verticalextent of the atmoshpere and continue along the geomagnetic lines offorce toward the conjugate point on earth. In other words, if a beam ofprotons having an initial energy of 3 bev. is directed vertically, i-twill pass through the atmosphere losing approximately 2 bev. (0.25 mev.per meter 8 kilometersX 1000 meters per kilometer), and have a residualenergy of 1 bev., whereby the protons will still be traveling atrelativistic velocity since their rest energy is 0.938 bev.

The-flux of particles, F, may be represented as:

where Nozthe number of particles emitted at the exit of the accelerator,

T :the time in seconds of the pluse duration, and

A=the cross-sectional area in cm.2 of the beam.

At the accelerator exit of the Argonne Zero Gradient Synchrontron, theflux is therefore 2 1016 particles per square centimeter per second.Since the ionization potential of air may be taken as 35 electron voltsper ion pair, the Argonne proton lbeam will generate 57,000 ion pairsper particle for every gram of air per cm.2 (8 meters) traversed, whichis approximately 7l ion pairs formed per cm.3 per particles at normaltemperature and pressure. The energy of each particle, as noted above,will be reduced by 2.5 103 mev. for each centimeter of air it tranversesas long as the particle is travelling at relativistic velocity. Thisenergy is spent almost en tirely on ionizing air molecules in its path.Therefore, the total number of free charge carries produced by the beamis substantial considering that 71 ion pairs (2.5 10-3 mev. per cm. 1/35ion-pair per electron volts) are generated by each particle as ittravels a centimeter and that there are 1013 particles transmitted perpulse.

At any instant, the number of ion pairs present per cm.3 can bedetermined by the equation:

where n=the number of ion pairs per cm,

q=the ion pair production rate per second per cm,

a=the recombination coehcient in cm.3 per ion pair per second and takenas equal to 1.6 l*6.

The computation of the ionization as a function of height in theatmosphere is complex even when secondary ionizations resulting fromnuclear interaction-s are disregarded. However, an approximatesemiquantitative calculation is used to indicate the order of magnitudeof ion concentration produced by a high energy proton beam.

As the proton beam'of the Argonne accelerator exits therefrom, it isdivergent with an angle of approximately 0.4 milliradian and dispersesfurther due t-o multiple scattering. It also becomes attenuated due tonuclear interactions. The ionization produced per unit volume thereforedecreases with increasing heights. The rate of ionization production isexpressed by the equation:

where p0=air density at NTP which equals l.293 103 grams per cm,

p=air density in grams per cm,

Z=height above ground in centimeters,

k=distance from beam exit to a virtual point source,

6=angular spread of the beam upon exit and equal to 0.4 milliradian,

71 :ion pair production per centimeter per particle as set forth supra,

L=absorption thickness, taken as 120 grams per cm?,

P0=atmospheric pressure at the surface taken in dynes per cm?,

P=atmospheric pressure at height Z in dynes per cm?,

g=acceleration of gravity taken as 980 cm. per sec?.

Integrating yields:

(exp. 21A/Ig) .1 1

This equation applies for a given height during the time required forthe beam to pass. After the beam has passed the given height, theionization production falls to zero .and the number of ions may beexpressed by the equation:

"D 1 -l-cmpt where np represents the number of ions due to electroniccollision just after the tail of the proton beam has passed. FIGURE 1illustrates the vertical profiles of ionization concentration based -onthe above equations with NACA standard atmosphere assumed. Graphs 10,12, 14, 16 and 18 are Iplots of the ionization concentration at times,10, 20, 30, 40 and 80 microseconds respectively after transmission ofthe beam from the accelerator exit. Ionization due to vmeson productionand other spallation reactions may yield total ionizations which areseveral times greater than that indicated in the graphs of FIGURE l.However, this would be counteracted by multiple scattering of the beam.Thus, the proton beam from the Argonne Zero Gradient Synchrotron may 'beused to produce a highly ionized beam or column from the surface of theearth to heights well above the tropopause.

As noted above, a proton having an energy of 3 bev. looses approximately2.5:10-3 mev. per centimeter of dry .air traversed. This ligurerepresenting the actual rate of energy los-s, is a function `of theparticular energy state of the particle, as is well known in the art.However, it can =be generally stated that the specific rate of energyloss remains nearly constant .as long as the particle is of an energy atleast as great as its rest energy, or in other words, is relativistic.Thus, t-he ion-pair generation will also be constant at 71 ion pairsgenerated. per centimeter traversed per proton for all energies abovethe rest energy. The rest energy of proton is '938 mev. For electrons,the corresponding value of rest energy is 0.51 mev. (or approximately1/1850 of the rest energy for a proton whichl is approximately the ratioof their respective masses).

While the actual rate of energy loss of changed particles is relativelyconstant for energies greater than the rest energy of the particle, itincreases 'appreciably for lower energies. This is well known in theart, as indicated in the graph on page 168 of Nuclear lPhysics, A.E.S.Green, McGraw-Hill Book Company, Inc., 1955. In this graph, the specificrate of energy loss :for protons is indicated for particular energies upto about 9 bev.; however, as a rst approximation, the curve may beextended to the 12.5 bev. energy value of the present example by simplelinear extrapolation as is indicated in the work of Aron, Hoffman andWilliams, ibid.

As noted above, it is desirable (for maximum ionization of the air) thatthe particles be travelling at relativistic velocity after traversing 8kilometers of atmosphere. The actual rate of energy loss for allrelativistic particles indicated. on the graph on page 168 of Green,ibid., except the alpha particle, is approximately 2.5 l0-3 mev. percm., as used in the .above example for protons. Hence, all suchparticles will lose approximately 2 bev. of energy in traversing 8kilometers of atmosphere; and, therefore, for maximum ionization, theparticles should have an initial energy at least .as great as their restenergy plus 2 bev. in order that they still be relativistic after theyhave traversed the 8 kiolmeters of atmosphere. However, it is noted thatcloud discharge will `occur even if the particles are not relativisticat the end of eight kilometers of travel as long as there exists acontinuous path of ionized particles between the cloud and the earth.The word discharge is used in the sense of reducing, and not necessarilyremoving, the charge of the cloud.

Turning now to FIGURE 2 wherein is shown an apparatus for the practiceof the present invention using a highly ionized beam generated lby theArgonne Zero Gradient Synchrotron as hereinbe-fore described. Everycloud has at least two charge centers and for the purposes of thepresent invention it is desirable that the lowest charge center of thecloud with respect to ground level be selected.

A network of electric eld meters 20 `are disposed symmetrically aroundthe accelerator 22. Assuming a cloud 24 has two charge centers, at leasteight eld meters should be used so that discrimination -between thecharge centers may be achieved. Electric eld meters and their use inmeasuring charge centers of clouds are well known in the art and hence adetailed description thereof will not be presented herein. Reference ismade to Some Theoretical Aspects of the Relation of Surface ElectricField `Observations to Cloud Chargel Distribution by D. R. Fitzgerald,Journal of Meteorology, pp. 505-512, Decem- 'ber 1957, and TheDistribution and Discharge of Thunderstorm Charge-Centers lby Reynoldsand Weill, Journal of Meteorology, pp. 1-12, February 1955. The electricfield Imeters 20 are placed in an essentially square arrangement withthe accelerator 22 at the center thereof. Each field meter 20 ispositioned so that the -measurement thereof is vertical, thereby givinga 2 1r Igeometry measurement.Y The output of each meter 20 is an A.-C.signal which is a function of the potential gradient in the regionbetween the cloud 24 and lground level at the iield meter position.

The output of each field meter 20 is fed to a computer 26 locatedadjacent the accelerator 22. The computer is preprogrammed to solve thesimultaneous equations which may be written for the output of each ofthe field meters 20 whereby the X, Y and H coordinates and the chargevalue of the charge centers of the cloud 24 are obtained. For a detaileddiscussion of these equations and their solution see D. R. Fitzgerald,ibid., pages 505 and 506. Though Fitzgerald illustrates only four fieldmeters in monopole detection, it is to be understood that the sametechniques and equations are used for a dipole or other arrangement, theonly variance bein-g in the number of simultaneous equations requiringsolution. Thus, by preprogramming the computer 26, the output therefromis a signal which is a measure of the spatial coordinates of the chargecenter of cloud 24 with respect to the accelerator 22. This signal isthen used in a manner hereinafter described to position the beam fromthe accelerator 22 so that it is directed at the determined chargecenter of the cloud 24.

As described supra the ionized column created by the beam provides a lowresistance path wherethrough the charge of the cloud 24 may bedissipated. The ionized column derived from the beam of accelerator 22causes considera-ble deformation of the electric eld which, if thecharge is high enough, will increase the potential gradient to valuesexceeding those necessary to create a spark discharge whereby thedischarge of cloud 24 via the beam from accelerator 22 will be in thenature of `a lightning stroke.

As shown in FIGURE 3, the output from the accelerator 22 is connected toa bending magnet 28. The bending magnet 28 is fixedly mounted and curvedso that the emerging beam from the accelerator 22 is caused to bendwhereby it is directed vertically into the atmosphere. A second bendingmagnet 30 is mounted on top of the bending magnet 2S so as to berotatable with respect thereto. The magnet 28 causes the beam to be bentinto a vertical direction and the magnet 30 by rotation and variation ofthe field thereof causes the beam to change direction in a regionbounded by a cone.

The bending magnet 28 to effect bending of the beam has a radius of `67feet and produces a field of 21,000 gauss. A cross-sectional view alonglines 4 4 of the magnet 28 is shown in FIGURE 4. The outer shell 32 isiron with the coil 34 being placed within interior spaces 3 5 and 36.The beam aperture 38 has a cross section of approximately 6 X 15".

Turning back to FIGURE 3, as previously stated, the bending magnet 30 ismounted so that it is rotatable with respect to magnet 28. To effectthis rotation the magnet 30 is fixedly mounted on a base plate 40. Theperiphery of the ibase plate has teeth 42 cut therein. The base plate 40is spaced from the bending magnet 28 by roller bearing supports 44 whichpermit rotation of the base plate 40. The base plate 40 an-d the bendingmagnet 30 both have apertures 46 therein to permit the passage of thebeam therethrough. The size of the apertures 46 is the same as that inthe bending magnet 28, namely, 6" x 15 The cross section of the magnet30 is the same as that shown in FIGURE 4 for magnet 28. The bendingmagnet 30 has a height of approximately 72" and produces a maximum fieldof approximately 20,000 gauss, thereby .giving the beam a conical sweephaving a half angle of 5.4 degrees.

As described supra, the output from the computer 26 is a signal which isa measure of the spatial coordinates of the charge center of cloud 24with respect to the accelerat-or 22. This output is fed through anamplifier 47 to a motor 48. Motor 48 in turn drives a spur gear 50engaged with the Igear teeth 42 cut into the periphery of the base plate40. The diameter of the spur gear 50 is small With respect to thediameter of the base plate 40 so as to permit incremental m-ovements ofthe base plate 40. Connected to the shaft of motor 48 via reductiongearing 51 is a synchro 52. The gearing S1 has a gear reduction suchthat the shaft -of synchro 52 has a positional movement the same as baseplate 40 for rotation of the shaft of motor 48. The stator of thesynchro 52 is excited from a power source 53 and the output voltagetaken from the rotor of the synchro is proportional to the rotativeposition of the base plate 40. The output of the synchro is fed back vtoan error sensing device 54 to provide a closed loop servo system for thepositional control of the base plate 40 responsive to the output of thecomputer 26. f

The -output of the computer 26 is also fed to a regulator 56 which inturn controls the output of a power supply 57 supplying the coils`of-magnet 30. By varying the power to the coils of magnet 30, the fielddeveloped therefrom is varied as is the angle through which Vthe beam isbent. Thus, the output from the computer 26 controls the angle throughwhich the beam is bent and the rotation of the base plate 40 whichdetermines the direction of the bending.

It is to 'be noted that the Argonne Zero Gradient Synchrotron hasduplicate outputs through which the beam may be ext-racted. Thus, whenno beam out-put is required for the present invention, the acceleratorbeam output yis diverted thro-ugh the second output.

In the present invention, therefore, the eld meters 20 furnishinformation to the computer 26, which according to the solution ofprepro-grammed simultaneous equations lgives a continuous output on thespatial location and charge value of a lcharge center within a cloud.The output 'from the computer 26 controls bending magnet 30, so thatwhen the output proton beam from accelerator 22 passes therethrough itis directed at the charge center of the cloud. The proton beam createsan ionized column extending from the accelerator to the charge center,through which the charge center discharges. As previously set forth, ifthe charge center in the cloud has a sufficient-ly high potential, thenthe discharge will be effected via an arc, or lightning discharge. Ifthe potential of the charge center of the cloud is not sufficientlyhigh, then the charge bleeds off to discharge the cloud. Thus, bymonitoring t'he measurement of the charge in the charge center obtainedfrom the computer 26 and electric field meters 20, t'he time of emittingthe beam from the accelerator may be controlled to prevent lightning byearly discharge of the bleeding type or to initiate lightning bydischarge when the charge of the charge center is high.

Since the discharge of the cloud is effected down the ionized pathcreated by the accelerator beam, the accelerator 22 must be protectedfrom the effects thereof. A Faraday cage 58 havin-g an aluminumstructure is mounted so that it surrounds the accelerator 22. The cage58 is grounded. Since the cage 58 is of a thin aluminum construction, itdoes not impede the transmission of the beam therethrough.

The above description was directed towards the use of the Argonne ZeroGradient Synchrotron and apparatus compatible therewith to effect themethod of the present invention. It is to be understood that the presentinvention lis not limited to such apparatus, but other accelerators maybe used as may other apparatus for controlling and directing the beam.Nor is it necessary that the ionizing beam be a proton beam. Forinstance, an electron beam may be used. Electrons have an advantage overprotons in that they remain relativistic to much lower energies;however, they also scat-ter more than protons.

Persons skilled in t'he alt will, of course, read-ily adapt theteachings of the present invention to methods far different than thoseillustrated. Accordingly, the scope of the protection afforded theinvention should not be limited to the methods ishown -in the drawingsand descri-bed above, but should be determined only in accordance `withthe appended claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A method of discharging to a predetermined location lon earth acharge-bearing cloud which is located Igenerally above saidpredetermined location and at an altitude of not more than eightkilometers comprising determining the spatial position of a chargecenter of said cloud relative to said predetermined discharge location,generating a beam of charged nuclear particles originating at saidpredetermined discharge location to form a column of ionized airextending a length suicient to reach from said predetermined location tosaid charge center, and directing said column at said charge center,whereby a continuous path of increased conductivity extends between saidcharge center and said predetermined disohange location.

2. The method of claim 1 wherein said step of generating a beam ofcharged nuclear particles comprises 8 transmitting a pulse ofapproximately 1013 protons hav-ing an energy of at least 3 bev., saidpulse having a crosssectional area of approximately 50 squarecentimeters and duration of approximately 10 microseconds.

3. The meth-od of claim 2 wherein said step of determining the chargecenter of the cloud comprises defining a pluraiirty -of ground positionsrelative to said predetermined discharge location, measuring thepotential gradients of each of said ground positions, and obtainingcoordinates of a charge center of said cloud relative to saidpredetermined discharge location from said potential ygradientmeasurements.

References Cited by the Examiner UNITED STATES PATENTS 3,019,989 2/1962Vonnegut 317-262 X MILTON `O. HIRSHFIELD, Primary Examiner.

LEE T. HIX, Examiner.

I. A. SILVERMAN, Assistant Examiner.

1. A METHOD OF DISCHARGING TO A PREDETERMINED LOCATION ON EARTH ACHARGE-BEARING CLOUD WHICH IS LOCATED GENERALLY ABOVE SAID PREDETERMINEDLOCATION AND AT AN ALTITUDE OF NOT MORE THAN EIGHT KILOMETERS COMPRISINGDETERMINING THE SPATIAL POSITION OF A CHARGE CENTER OF SAID CLOUDRELATIVE TO SAID PREDETERMINED DISCHARGE LOCATION, GENERATING A BEAM OFCHARGED NUCLEAR PARTICLES ORIGINATING AT SAID PREDETERMINED DISCHARGELOCATION TO FORM A COLUMN OF IONIZED AIR EXTENDING A LENGTH SUFFICIENTTO REACH FROM SAID PREDETERMINED LOCATION TO SAID CHARGE CENTER, ANDDIRECTING SAID COLUMN AT SAID CHARGE CENTER, WHEREBY A CONTINUOUS PATHOF INCREASED CONDUCTIVITY EXTENDS BETWEEN SAID CHARGE CENTER AND SAIDPREDETERMINED DISCHARGE LOCATION.